How to get random letters in a multidimensional array in Python? [closed]

I'm new to Python and I'm trying to translate some code from c++ to python, but I can't make letters be random in both dimensions of a list. This is my function

def chooseLetter():
    lower_alphabet=['a', 'b', 'c', 'd']
    element=''
    if (random.randint(0,2)==1):
        element = element + random.choice(lower_alphabet)
        return element
    else:
        return ' '


for i in range(9):
for j in range(9):
    board[i][j]=chooseLetter()

I get something like this

[[' ', 'b', 'b', 'c', ' ', ' ', ' ', ' ', ' '], [' ', 'b', 'b', 'c', ' ', ' ', ' ', ' ', ' '], ...

I tried system random and some datetime modules, but I am not that familiar with all that and it doesn't really work. ' ' are supposed to be there, I don't want letters to be everywhere.